With Datacenter, Hyper-V and multi-core, I've cut my Windows costs by 90% in 1 year. I don't even need blades. 3850's crammed with memory do just fine and simplify support with scalable I/O, standard drivers, fantastic cooling, and big proc cache. Don't forget hex-core.

This is by far the easiest and best kept secret. You can even just purchase Datacenter for a VMware host, then all the Window's VM's on that ESX box are free.